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Derivatives - NSM Interest Rate Swap (Details) - USD ($) | 3 Months Ended | 5 Months Ended | 9 Months Ended |  |
--- | --- | --- | --- | --- | ---
Sep. 30, 2018 | Sep. 30, 2018 | Sep. 30, 2018 | May 11, 2018 | Dec. 31, 2017
NSM Holding Co LLC | NSM Bank Facility |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Total commitment under revolving credit facility |  |  |  | $ 100,000,000 |
Term Loan | NSM Holding Co LLC | NSM Bank Facility |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Face amount | $ 150,600,000 | $ 150,600,000 | $ 150,600,000 |  | $ 0
Debt, weighted average interest rate, all-in | 6.69% | 6.69% | 6.69% |  |
Interest Rate Swap | NSM Holding Co LLC |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Derivative, fixed interest rate | 2.9745% | 2.9745% | 2.9745% |  |
Derivative, variable interest rate | 2.07% | 2.07% | 2.07% |  |
Interest expense, net | $ 300,000.0 | $ 400,000.0 |  |  |
Derivative, fair value, net | 100,000.0 | $ 100,000.0 | $ 100,000.0 |  |
Change in fair value of derivative | $ 1,000,000.0 |  | $ (100,000.0) |  |
Interest Rate Swap | Term Loan | NSM Bank Facility |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Derivative, variable interest rate | 2.07325% | 2.07325% | 2.07325% |  |
Interest Rate Swap | Term Loan | NSM Holding Co LLC | NSM Bank Facility |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Derivative, fixed interest rate | 2.9745% | 2.9745% | 2.9745% |  |
Debt, weighted average interest rate, all-in | 7.47% | 7.47% | 7.47% |  |
Margin over London Interbank Offered Rate (LIBOR) | Minimum | Term Loan | NSM Holding Co LLC | NSM Bank Facility |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Basis spread on variable rate | 4.25% |  |  |  |
Margin over London Interbank Offered Rate (LIBOR) | Maximum | Term Loan | NSM Holding Co LLC | NSM Bank Facility |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Basis spread on variable rate | 4.75% |  |  |  |
Margin over Prime Rate | Minimum | Term Loan | NSM Holding Co LLC | NSM Bank Facility |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Basis spread on variable rate | 3.25% |  |  |  |
Margin over Prime Rate | Maximum | Term Loan | NSM Holding Co LLC | NSM Bank Facility |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Basis spread on variable rate | 3.75% |  |  |  |

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- Definition Amount of gain (loss) from the increase (decrease) in fair value of derivative and nonderivative instruments designated as fair value hedging instruments recognized in the income statement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 25 -Section 50 -Paragraph 1 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=109977999&loc=d3e76258-113986 + Details
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- Definition Fair value of the assets less the liabilities of a derivative or group of derivatives. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=109250915&loc=d3e13433-108611 + Details
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